1. Field of the Invention
The present invention relates to an analog-to-digital converter for a camera and, particularly, it relates to an analog-to-digital converter (hereinafter referred to as A-D converter) for effecting analog-to-digital conversion (hereinafter referred to as A-D conversion) of a photometric output of a light measuring device of a camera, thereby obtaining a photometric value in the form of a digital signal.
2. Description of the Related Art
Recently, a digital exposure control has become widely used in a camera and, accordingly, a light measuring device of the type in which an analog signal of a photometric output of the light measuring device is converted into a corresponding digital signal by means of an A-D converter whereby a photometric value is obtained in the form of a digital value is frequently used in a camera.
Such an A-D converter is disclosed, for example, in U.S. Pat. Nos. 4,265,521, 4,167,312, 4,162,839, 4,462,673, 4,363,540, 4,370,037, 4,480,902, 4,455,069 and 4,103,307.
In order to reduce a time required to effect the A-D conversion, the A-D converter circuit used in the light measuring device is preferably constructed in the form of a sequential comparison type in which a relatively short time is required to effect the A-D conversion.
The A-D converter of this type, however, includes a resistor array, as its indispensable component, and, consequently, an error in reading a voltage in the order of a few LSB is necessarily caused owing to such factors as irregularities of resistor elements or the like.
For example, the A-D converter circuit of 8-bit type, in which its full range is from 0(V) to Vfull (V), has a resolving power of Vfull/256, and if it is assumed that there is an error of nLSB, the voltage reading error of n.times.Vfull/256 is caused. In this instance, nLSB is a characteristic value of the circuit and, therefore, the nLSB indicates a characteristic error. In order to reduce such error, it is required to reduce the full range.